This invention relates generally to lubrication means enabling both metal and/or ceramic bearing surfaces to resist mechanical wear at elevated temperatures of at least 300.degree. C. and higher, and more particularly to employing an improved source of lubrication as the means for doing so.
Lubrication is a well recognized means to reduce friction and wear between bearing surfaces in dynamic physical contact. As such, a pair of load bearing surfaces having relative movement therebetween will be in rolling or sliding contact, as well as combinations thereof, which can include a wide variety of known structural articles such as journal bearings, piston rings, gears, cams and the like. Two major areas for which improved lubricants are needed for continued progress are metal-forming and transportation. Better metal-forming capabilities to minimize machining and grinding require lubrication techniques and lubricants that can be used effectively at temperatures approaching the melting points of the metals now employed. In transportation, one of the most productive areas for increasing energy efficiencies is often referred to as high temperature engines wherein temperatures range from 300.degree. C. and above making the selection of lubricants and means of lubrication difficult. In other known bearing applications, high bearing contact pressures of 70,000 psi are experienced making lubrication most difficult with existing lubricant systems. A known technique for lubrication at such high bearing temperatures and pressures is the use of solid lubricants in the form of plasma sprayed coatings of metals and ceramics being employed. More recent developments whereby an adherent solid polymeric lubricating film is deposited on a ferrous metal surface to afford such protection are reported in technical publications entitled "In situ Formation of Solid Lubricating Films from Conventional Mineral Oil and Ester Solid Lubricants" authored by N. deGouvea Pinto, J. L. Duda, E. E. Graham and E. E. Klaus, ASLE Proceedings, 3rd International Conference on Solid Lubrication, ASLESP-14, 1984 and "Lubrication from the Vapor-Phase at High Temperatures", authored by E. E. Graham and E. E. Klaus, ASLE Transactions, Volume 29 No. 2, pages 229-234 (1986). As described in the said technical publications the metal surfaces are deemed to have a catalytic effect upon the vapor-phase reactants whereby surface polymerization of said reactants takes place to produce the protective film. Possibly the absence of comparable metal catalytic agents in ceramic materials has prevented the formation of the protective film in such manner. More particularly, a vapor-phase deposition of the same reactants under the same process conditions have thus far only produced non-adherent surface deposits affording no substantial protection to the underlying ceramic substrate.
Improved vapor-phase lubrication of ceramic bearing devices with a more adherent organic polymer film is disclosed in a co-pending U.S. patent application Ser. No. 07/488,984 entitled "Ceramic Article Having Wear Resistant Coating", filed Mar. 5, 1990 in the names of E. E. Graham and J. F. Makki, and now U.S. Pat. No. 5,139,876. Formation of a tenacious lubricating film is achieved upon treating the uncoated ceramic surface at elevated temperatures with activating metal ions to form a deposit of the activating metal ions on the ceramic surface and thereafter exposing the treated ceramic surface to a vaporized polymer-forming organic recactent at elevated temperatures whereby an adherent solid organic polymer lubricating film is produced on the treated surface. Bearing surfaces formed with crystalline ceramic materials such as silicon nitride and silicon carbide as well as vitreous ceramics such as fused quartz can be provided with a protective coating resistant to dynamic wear conditions up to at least 500.degree. C. and higher in this manner. In one embodiment, activating metal ions comprising a transition metal element selected from the Periodic Table of Elements, to include iron and tin are initially deposited at temperatures of at least 300.degree. C. on the ceramic surface. Formation of a lubricating film on the treated ceramic surface is achieved with vapor deposition again conducted at elevated temperatures of approximately 300.degree. C.-800.degree. C. of various polymer forming organic reactants such as petroleum hydrocarbon compounds, mineral oils, various synthetic lubricants and to further include tricresyl phosphate (TCP) and triphenyl phosphate.
In a still more recently filed U.S. patent application Ser. No. 07/739,402, entitled "Metal Oxide Lubrication for Ceramic Bearing System", filed Aug. 2, 1991, in the name of E. E. Graham, and now U.S. Pat. No. 5,162,757 there is disclosed lubrication means for ceramic bearing devices utilizing metal oxide lubricants formed during bearing operation. As therein disclosed, continuous lubrication of the ceramic bearing surface is provided with solid metal oxide lubricants formed in situ with an oxidizable metal source located in physical proximity to the ceramic bearing surfaces being treated. A representative lubrication system enabling such mode of operation includes (a) support means causing the ceramic bearing surfaces to be maintained in dynamic physical contact, (b) an oxidizable metal source located in physical proximity to the support means, and (c) heating means for continuously heating the metal source while the ceramic bearing surfaces are being operated sufficient to provide the solid metal oxide lubricants. In one embodiment, the ceramic bearing means employs ceramic ball bearings supported within a ceramic race with a metal housing member enclosing the bearing structure. Utilizing oxidizable metals for construction of said housing member, including molybdenum and iron alloys, provides a suitable metal source in sufficient physical proximity to the bearing surfaces for satisfactory lubrication at the aforementioned operating conditions.
It remains desirable to provide lubrication of both metal and ceramic bearing means when operated at these elevated temperatures under atmospheric conditions by still more effective means. Accordingly, it is one object of the present invention to provide improved lubrication means for various type mechanical apparatus utilizing either metal or ceramic bearing materials, including combinations thereof, under such operating conditions.
It is another object of the present invention to provide means for continuous lubrication of metal and ceramic bearing surfaces with novel polymer lubricants formed in situ.
A still further object of the present invention is to provide a novel method for the lubrication of metal and/or ceramic bearing surfaces at relatively low lubricant levels with vapor-phase deposited lubricants.
These and further objects of the present invention will become apparent upon considering the following detailed description of the present invention.